1. Field of the Invention
The present invention relates to fuel cells and, more specifically a porous solid oxide fuel cell for electricity and syngas co-generation.
2. Description of the Related Art
Fuel cells provide a clean and versatile means to directly convert chemical energy to electricity. Among the many types of fuel cells, solid-oxide fuel cells (SOFCs) have received considerable attention owing to their simplicity (no moving parts), fuel flexibility and use of inexpensive catalytic materials.
Among many fuel cell configurations, the development of single-chamber SOFCs (SC-SOFCs) has generated widespread interest due to its simple configuration in which both the anode and cathode of the cells are exposed to the same fuel-oxidant gas mixture. In this simple, one-chamber configuration, no sealant is necessary and the cell can be rapidly heated and cooled. The operation of this kind of fuel cell is based on the different catalytic selectivity of the anode and cathode. Under ideal conditions, the cathode reacts only on the oxygen activation, while the anode reacts only on the partial oxidation of fuel. The different catalytic selectivity of anode and cathode leads to an oxygen partial pressure gradient which drives continuous power output. Extensive studies have been conducted to improve the power output and systematic configurations of SOFCs and high power output which is comparable to dual chamber SOFCs (DC-SOFCs) has been achieved. However, SC-SOFCs requirement of fuel rich conditions for operation prohibits its application as excessive fuel must be supplied and wasted, thereby lowering system efficiency. Also, whether through thermal power or conventional fuel cells, power generation and the chemical energy conversion process of hydrocarbon fuels involves the emissions of CO2 greenhouse gases.
If excessive hydrocarbon fuels could be simultaneously converted into value-added chemical products (like syngas) during electricity generation instead of CO2, higher energy conversion efficiency could be expected along with zero emissions of environmental pollutants. Some researchers have shown the generation of electricity while simultaneously converting the fuel into value-added chemical products through a DC-SOFC reactor. However, using a DC-SOFC for gas co-generation is confronted with the problem that product selectivity and yield is restricted by the operating conditions of the fuel cell. Changes in the polarization current lead to significant changes in product composition and yield. Also, the direct exposure of the anode to pure hydrocarbons presents a serious coking problem. Similarly, electricity and syngas cogeneration systems based on conventional SC-SOFCs are capable of high power output and high syngas production but suffer from some drawbacks. For example, the oxidation reaction of fuel and oxidant is non-homogeneous distributed across the fuel cell, resulting in a high temperature gradient that can crack the fuel cell itself. In addition, only a small amount of the fuel can be utilized since most of fuel just passes through the fuel cell, thereby resulting in low fuel utilization and fuel concentration polarization losses. Furthermore, the current design of SC-SOFC system is that the fuel and oxidant flow is parallel to the fuel cell, resulting in low OCVs, as the utilization of oxygen in the upstream may result in the lack of oxygen at the cathode at the downstream. Finally, to get syngas production, a downstream catalyst is required which increases the complexity of system design. Thus, there is a need in the art for an improved electricity and syngas co-generation system that does not suffer from the drawbacks of conventional systems.